1. Field of Invention
The present invention relates to a fabricating method of a circuit board, and more particularly to a fabricating method of a multi-layer circuit board.
2. Related Art
A circuit board fabricated by a present circuit board process usually has a symmetrical structure. That is to say, the number of the circuit layers is mostly even, e.g. two layers, four layers, or six layers, but the circuit board having an odd number of layers equal to three or more than three is seldom fabricated.
FIG. 1A to FIG. 1F are schematic sectional views of process flow of a conventional fabricating method of a circuit board. Referring to FIG. 1A, the conventional circuit board fabricating method includes the following steps. First, a copper-clad laminate (CCL) 110 is provided, wherein the CCL 110 includes a resin layer 112 and two copper layers 114, and the resin layer 112 is disposed between the two copper layers 114.
Referring to FIG. 1B, next, a laser drilling process is used to form at least one blind via V1 in the CCL 110, and the blind via V1 penetrates the resin layer 112 and partially exposes one of the copper layers 114.
Referring to FIG. 1C, a plating hole process is performed in the blind via V1, so as to form a copper column 120 in the blind via V1, and the copper columns 120 connect to the copper layers 114.
Referring to FIGS. 1C and 1D, the copper layers 114 undergo a lithographic process and an etching process to remove a part of the copper layers 114 and further to form two circuit layers 122 that partially expose the resin layer 112.
Referring to FIG. 1E, then, two prepregs 140 and two copper foils 150 are respectively laminated on the circuit layers 122, in which each prepreg 140 adheres to one copper foil 150 and one circuit layer 122, and the prepregs 140 are respectively located on two opposite sides of the resin layer 112.
Referring to FIG. 1F, a plurality of copper columns 160 are formed in the prepregs 140, and the copper columns 160 connect to the circuit layers 122 and the copper foils 150. The copper columns 160 may be formed in the method which is the same as the copper columns 120, and the details will not be repeated herein again.
Referring to FIGS. 1F and 1G, then, the copper foils 150 undergo a lithographic process and an etching process to remove a part of the copper foils 150 and further to form two circuit layers 152 that partially expose the prepregs 140. Till now, a circuit board 100 having four circuit layers (i.e. two circuit layers 122 and two circuit layers 152) is complete.
It can be seen from the above that the current circuit board process is mostly applicable to fabricating the circuit board having an even number of layers. However, as technology advances, the circuit design of the circuit board becomes more various, so that the demands for the circuit board having an odd number of layers increase. Therefore, how to achieve the mass fabrication of the circuit board having an odd number of layers has become a topic to be researched.